prism
A TUI RGB color picker. Two slots (foreground + background), R/G/B
and H/S/V sliders, hex input, live sample-text preview, WCAG contrast
indicator. Pure ANSI 24-bit truecolor — no kitty graphics dependency,
works in any modern terminal.
Member of the Fe₂O₃ Rust terminal
suite (landing page).
Features
- Two color slots. Edit foreground and background side-by-side,
Tab to swap which one is active.
- RGB and HSV at the same time. Six sliders share one underlying
color: nudge the hue and the R/G/B values move with it; nudge red
and the hue/saturation/value follow. Pick whichever axis fits the
job.
- Hex input. Press
#, type six hex digits, Enter.
- Live sample text. A multi-line sample area renders the current
FG-on-BG against realistic content (heading, code, comments, body
prose, special characters), so you immediately see whether the
pair is readable.
- WCAG contrast. The contrast ratio between FG and BG is shown
with a level marker (
AAA ≥ 7 / AA ≥ 4.5 / AA· ≥ 3 / ✗ low),
so theme work doesn't ship unreadable pairs.
- Pipe-friendly output. On quit, the chosen colors are printed
to stdout in your chosen format (hex / rgb / hsv / all). Use it
to drive
sed against a config file, or capture a single hex
with prism --pick.
- Tiny. ~500 KB stripped binary. ~5 MB resident. No async
runtime, no allocator hot path, no work between keystrokes.
Install
PATH="/usr/bin:$PATH" cargo build --release
ln -sf "$(pwd)/target/release/prism" ~/bin/prism
Usage
prism # interactive (pair mode, prints both slots)
prism --pick # pick a single color (the FG slot)
prism --pair # explicit pair mode (the default)
prism --hex # output as #rrggbb (default)
prism --rgb # output as rgb(R, G, B)
prism --hsv # output as hsv(H°, S%, V%)
prism --all # output all three formats
prism --out=FILE # write the result to FILE instead of stdout
prism #f74c00 # preload FG with this hex
prism #f74c00 #0a0a14 # preload both FG and BG
On quit, the chosen colors print to stdout one per line, prefixed
with the slot name (or to --out=FILE — see below):
$ prism --pick
color=#f74c00
$ prism --pair --rgb
fg=rgb(247, 76, 0)
bg=rgb(10, 10, 20)
This makes prism easy to script against:
# Update glassrc fg color
hex=$(prism --pick #$(grep '^fg=' ~/.glassrc | cut -d# -f2) | cut -d= -f2)
sed -i "s/^fg=.*/fg=$hex/" ~/.glassrc
To embed prism as a colour picker inside another TUI, use --out=FILE:
prism draws on the terminal as usual, but writes the result to the file
instead of stdout, so the host app's screen and prism's UI don't collide.
The caller launches prism --pair --out=/tmp/pick $FG $BG, then reads the
chosen colours from the file (this is how grid
colours cells).
Keys
| Key | Action |
|---|
Tab | swap which slot (FG / BG) is being edited |
r g b h s v | focus that channel |
j / ↓ / ← | step focused channel −1 |
k / ↑ / → | step focused channel +1 (V past 100 goes on toward white) |
J / Shift-↓ / Shift-← | step −10 |
K / Shift-↑ / Shift-→ | step +10 |
# | type a hex value (then Enter) |
c | copy current hex to clipboard |
o | cycle output format (hex → rgb → hsv → all) |
t | paint the terminal's background in the current colour, t again puts it back (OSC 11) |
q / Esc | quit |
Footprint
- ~500 KB stripped binary
- ~5 MB resident
- Pure ANSI 24-bit truecolor, no kitty graphics dependency
- No subprocess spawns once running, no polling
Compatibility
Works in any terminal that handles 24-bit truecolor SGR escapes:
- glass, kitty, wezterm, foot, alacritty, st, xterm (with 256 + Tc),
iTerm2, Apple Terminal (modern)
- tmux: requires
set -g default-terminal "tmux-256color" and
set -ag terminal-overrides ",xterm-256color:RGB" so SGR 38;2/48;2
passes through
Why "prism"
A prism splits white light into its component colors. The picker
splits a single hex value into its R / G / B and H / S / V channels
so you can dial each axis independently while watching the result
on real text.
Part of Fe₂O₃
License
Unlicense (public domain). Borrow or steal whatever you want.
